Riepsamen AH, Donoghoe MW, Baerwald A, et al. - Researchers conducted a cross-sectional, observational, and exploratory study in order to describe and evaluate the changes in serum concentrations of oocyte-secreted growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) throughout the menstrual cycle in women from young to advanced reproductive ages. From 3 cohorts of healthy, ovulatory women, serum was obtained every 1–3 days throughout the menstrual cycle for this analysis: menses to late luteal phase (21–29 years of age; n = 16; University of Otago) and across one interovulatory interval (18-35 years of age; n = 10; and 45–50 years of age; n = 15; University of Saskatchewan). Fifty-four percent and 73% of women had detectable GDF9 and BMP15, respectively, and their concentrations varied 236-fold and 52-fold between women, respectively. Findings revealed no statistically detectable serial changes in GDF9 or BMP15 concentrations across the cycle and these are likewise similar across the reproductive lifespan.